wiredsoftware

Edit: updated diagram to put the relay AFTER the fuse, which minimises the length of circuit that is fused at the higher amperage.

The current will be flowing through the whole circuit, so all parts of it will experience the stress of the current, so either could fail if they are equal. Really you should only need one fuse on the whole circuit, as exceeding the fuse's rating should cause it to fail regardless of where in the circuit the failure happened. Given a short in the seat that caused it's resistance to be substantially reduced, the resistance drops but voltage stays the same. By ohms law, the current would rise. As the battery's resistance is low, and the wire resistance is also low, you'd create an almost resistance free path round the circuit, creating a very effective heating element of hot wires. To prevent this, the fuse melts at 15A, severing the whole circuit. You know the wires can handle that amount, and the relay can, and the seats can, so it's the weakest link and fails before anything else melts. Having two fuses on the same circuit just means that the one with the lowest rating fails first. With both the same rating, which fails first is pot luck as they are both going to see the current for similar amount of time, be in places with slightly different cooling/temperature, and also have slightly different manufacturing impurities. As Wino mentions above, you DO need a fuse as the 110A one for the bus bar is too high to (literally) save your ass, but this will be the one you have added to the fuse box.

I assume you're putting that inline fuse somewhere you can access it if the seats overload? As it'll be probably be the one that pops, not the one in the fuse box (assuming you're talking about putting this on the high current circuit through the relay, if on the low side then ignore me!).

Or buy a Fabia 1.9 TDI with 12mths MOT on it for £900: http://www.ebay.co.uk/itm/Skoda-Fabia-1-9TDi-Comfort-Estate-Red-MOT-FEB-2017-No-Advisories-/182004743266?hash=item2a6053fc62:g:MgYAAOSwvUlWqNPE Couldn't resist saying it

As long as you are using the same gauge as the fan is from battery to fuse box for the relay arrangement, you'll easily handle the seat heater loads, and the fuse will prevent any damage to your buttocks if the heater itself shorts.

Here's one with connector and integrated fuse: http://www.ebay.co.uk/ulk/itm/291613194408 Fine to use spade connectors instead if you want, as long as you mount somewhere where they cannot move around and touch ground

Yes. You want a four or five pin relay (if you get a 5 pin, just ignore pin 87a, don't need it for your job). 12v auto relays are generally rated for 30-40a so should work nicely. Basically, they work by switching on a separate circuit when another circuit is on. Both circuits are separate and can work on different loads and voltages. The type you'll get also make a characteristic click noise when they make the circuit, so you can test that you've got the low current side done correctly before you move the wires for the high current side if you wish by listening for this. Incidentally you mention about putting 15a fuse inline. I'd go higher on this, say 25A as it is only there to protect the relay. If 24.99A is pulled through, the relay will be fine, the 15a in the fuse box will blow instead to protect the seats with no harm done, which will probably be easier to access!

Adding fuses at any point you show in your diagram won't help. If you add the 25 before the fuse box, it'll blow if both are on (assuming together they draw a bit under 40). Adding a 15 between the two points on the fuse box doesn't help either, it just means two equal fuses on the same path. The relay option would work quite well, run the heavy duty path of the relay through the 15a, and you can probably get away without an additional fuse for the low current side just using an existing switched live that is after some fuse already.

Also, unless I've read it wrong, wouldn't option B be just two 15A fuses in series, with the possibility of 40A on the earlier stretch still?

Could you not take a new wire from one of the beefy terminals above the comfort module?

At least one of those blue connectors seems to be on the "black with blue stripe" wire. That wire is the permanent live that runs directly from fuse 45 in the fuse box. I'd be very suspicious of whatever that is giving power to. If you need to move it to a switched live, I think it's the wire that's brown with red stripe on connector A to the head unit is switched with the ignition. Make sure you get the one from the right connector, as there is one of the same colour on the speaker connector!

What are those blue connectors for? Looks like maybe an aerial booster? (Edit: see my next post)

Current fuse is 20A, obviously it's relay driven so any increase would only be on that circuit. I can't comment on whether the wiring will handle that horn as it says 20-30A, at the top end you'd need a bigger fuse and you'd be pulling 50% more current. Even at 20A, you're on the limit. That being said, horns obviously are usually deployed momentarily, and you'd get your message across quickly with that. Worth risking melting your insulation? Your call

The U281 is great at what it does: reading fault codes, and clearing them. However, that's all it can do. If you needed to change any settings, you need VCDS of some version. The U281 is good if you've got a fault - you scan for the code, go on here and search for the code, buy the suggested parts to fix, fit them, and clear the codes. A good example of something that you would use VCDS for is installing an optional extra from a higher spec model e.g. Heated seats, so you can enable it in the control unit of the car. Another example might be modifying comfort options like whether unlocking the car unlocks only one door or all at once. Both VCDS and the Lite version both do lots of useful stuff. The Rosstech site lists the differences between the versions. The website also tells you what cable you need to buy.

Got rid of a dead Zafira recently, got £50 for it as it had alloys and good tyres. The scrappie only offered £25 if the tyres were not good. Obviously that car is twice the size of a Fabia, so best off selling it with some MOT on it.

Yeah should work fine and mount easily, although you'll need to chop off the factory Skoda connector on the loom, and wire your own generic spade connectors.

Easy enough job, if a little fiddly. Remove the bumper - there are screws in each wheel arch and across the bottom of the bumper, and some push-through plastic rivets. You'll probably have a much easier time if you can jack the front up a metre. Once the bumper is off (you can leave the fog lights attached as it foesnt need to go off fully), the horn(s) is right there. Each horn is attached to a bracket by one nut, and the wire connectors can be freed by hand or with a carefully placed flat blade. Swap for new ones, reassemble.

Weird, for some reason there's a space at the end of the link. Try this instead: http://www.engineeringtoolbox.com/wire-gauges-d_419.html

Had this all wrong - the end that is captive is on the chassis side - so to replace this you have to remove at least part of the dash and side kick trim in the car, but don't have to remove door trim at all

On the fuse box layout, it looks like they should go through fuse 63, with a 15A fuse. Wire gauge to max amps chart, might help if you know gauge and no. of cores: http://www.engineeringtoolbox.com/wire-gauges-d_419.html

Yes, just dreading having to scrape off all that old sealant that's already on there

Great, thanks. I guess I'll have a look at slackening off the bolts and seeing if I can wiggle it out without going via the carrier, but looking at the pic I suspect the hole is too small. Thanks for the eBay link too. At least I have the bolt-on carriers, not riveted ones.

Hey, my driver's door swings open and closed much easier than the others, parking on the slightest incline and it will slam shut on you as you get out of the car. I guess it's that the notched bar (name?) that holds the door in place has worn down from use (as it's the most used door), the notches do seem a bit flatter than those on the other doors. Is this part serviceable/adjustable/replaceable/swappable from the other doors? Is it a big job, and do you need to take the door covers/internal panels off? Would prefer not to do that as I've sealed them! Thanks.

Confusingly, there's universal (as in fits in anything), and ISOFIX's "universal", which means it fits any full ISOFIX (which should include top mounts). ISOFIX's "semi-universal" means bottom mounts only and some sort of bracing leg. There's also manufacturer-specific ISOFIX, which are seats designed for specific vehicles only. As the kids get older they usually move on to a booster seat that uses the built in seatbelt for restraint, so ISOFIX is not really important for those as long as it's not just a lap belt, as the seatbelt takes care of making sure you are supported both on chest and waist so you can't rotate. As long as your (bottom only) ISOFIX booster uses the seatbelt across the chest (or it's own harness), it's good. The boosters with backs are probably best as they provide some side-to-side protection for the head on side impacts. And then there's "ISOFIT", oh yeah and boosters that have their own straps, and also.....

Bought that set a month ago. Quick delivery, seems alright (not fitted them yet though). Includes adapters and loads of different screws and brackets to mount. Note that the ad mentions "2x crossovers" - this is simply an in-line filter on the tweeter cables, so isn't truly a crossover. There is no filtering of the signal to the main speakers (on the short adapter cables I mean). The inline capacitor is rated at 3.3uF, which at 4ohm I think gives you about 12kHz filtering.